ESR spectra were recorded by the static or flow method in the course of the alkaline autoxidation of catechol and pyrogallol. Although water or ethyl alcohol was used in the oxidation of catechol as solvent, ESR spectrum composed of 9 signals was recorded by the static method. However, by the flow method, the distinctive hfs of o-benzosemiquinone anion radical with the relative intensity of 1:2:1:2:4:2:1:2:1 was observed, even water, N, N-dimethylformamide, methyl alcohol or ethyl alcohol had been employed as the solvent. The ESR spectrum has the coupling constants about 3.6 gauss and 0.8 gauss. On the other hand, in the oxidation of pyrogallol, ESR spectrum having 2 signals with the coupling constant 5.0 gauss was recorded by the static method only in ethyl alcohol as solvent. However, by the flow method, hfs of 2 groups of the triplet was observed. The ESR spectrum was presumed to be formed by tripling (1:2:1) of each signal with the coupling constant of 0.96 gauss.